<!DOCTYPE html>
<html >
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS执行机制</title>
</head>
<body>
    
</body>
<script>
     console.log(1);
     console.log(2);
     setTimeout(() =>{
        console.log('我来了');

    },3000);
     console.log(3);
     console.log(4);
 
    
    
    
</script>
</html>